Various methods are proposed for manufacturing optical fiber glass in a continuous process. One method is that disclosed in U.S. Pat. No. 3,957,474 assigned to Nippon Telegraph and Telephone Public Corp. This method involves the deposition of the glass forming ingredients on a heated mandrel to form a fiber optic preform.
The method described in U.S. Pat. No. 3,614,197 assigned to Semiconductor Research Foundation describes the process of using a multi-stepped funnel-shaped heating vessel to form a solid glass rod which is subsequently heated and drawn into an optical fiber. Both the heated mandrel and the heated crucible process provide continuous means for forming optical fiber glass into a solid glass preform but do not suggest forming the optical fiber per se in an in-line continuous process where the raw materials are fed into one end of the process while a finished optical fiber is continuously drawn from the other end.
It was first believed that the formation of a solid optical fiber preform as a separate step in the fiber manufacturing process provided certain beneficial results. The rod could be tested for optical transmission properties as well as geometric uniformity before being drawn into a fiber. These measurements could be used to select the best candidates from a number of fiber optical preforms before investing time and effort into drawing large quantities of the resultant optical fibers.
The purpose of this invention is to provide methods and apparatus for forming high strength and high purity optical fibers in a single continuous manufacturing operation.